This invention relates to an adjustable housing for a mud motor and more particularly to an adjustable housing for directional drilling of well bores.
U.S. Pat. No. 5,048,621 to Bailey et al provides an adjustable bent housing for controlled directional drilling of well bores. The bent housing comprises a first sub rotatably mounted to a second sub for adjustment of an angle therebetween. An end portion of the outer surface of the first sub and an end portion of the inner surface of the second sub have annular offsets from the central axes of the subs to allow angular adjustment when one sub is rotated relative to the other. Once the desired angle has been set, rotation of the first sub relative to the second sub is prevented by an adjusting ring which includes both internal and external splines for engaging splines on both first and second subs. The adjusting ring however is axially aligned with the first sub and thus engages the spines on the second sub at the offset angle. The adjusting ring therefore is not evenly secured across its entire end face to the second sub. Machining the complex spline structure and the surfaces at an offset angle is a costly and difficult procedure.
According to the present invention there is provided an adjustable housing for use with a mud motor, the adjustable housing comprising:
an upper sub comprising a top portion having a primary longitudinal axis, a bottom portion having a secondary longitudinal axis offset from the primary longitudinal axis by a first predetermined angle and a first set of splines extending axially along an outer surface of the bottom portion,
a lower sub comprising a lower portion having a primary longitudinal axis, a top portion having a secondary longitudinal axis offset from the primary longitudinal axis by a second predetermined angle and an engaging face on a top end of the top portion perpendicular to the secondary axis of the lower sub;
mounting means rotatably mounting the bottom portion of the upper sub on the top portion of the lower sub such that the secondary axes are coincident and the upper sub is rotatable relative to the lower sub;
an annular locking member mounted coaxially on the bottom portion of the upper sub, the locking member having a second set of splines extending axially along an inner surface of the locking member and engaging the first set of splines for sliding movement on the bottom portion of the upper sub between an engaged position wherein an end of the locking member engages the engaging face to prevent rotation of the upper sub relative to the lower sub and a disengaged position wherein the locking member does not engage the engaging face such that the upper sub is free to rotate relative to the lower sub; and
lock securing means for securing the locking member in the engaged position.
The advantage of this arrangement is that the locking member and a portion of each sub are all coaxial for rotation about the same axis. The locking member engages an end engaging face that is perpendicular to that axis and not offset.
Preferably there is provided a first set of teeth on the end of the locking member and a second set of teeth on the engaging face of the lower sub, the first and second sets of teeth being arranged to engage each other for locking the subs together in the engaged position, regardless of the relative orientation of the two subs.
For mounting the adjustable housing in line with a drill string there is preferably provided a threaded section on a top end of the upper sub and a threaded section on a bottom end of the lower sub.
The lower portion of the upper sub preferably has a reduced diameter for being received coaxially within the upper portion of the lower sub.
The mounting means may comprise a threaded section having an annular groove at an end thereof for allowing longitudinal displacement of the upper sub relative to the lower sub as the upper sub is rotated relative to the lower sub.
Preferably there is provided at least one annular seal mounted about an outer face of the bottom portion of the upper sub, the seal being arranged to engage an inner face of the top portion of the lower sub for sealing between the subs.
The lock securing means may comprise a locking nut threadably mounted coaxially on the lower portion of the upper sub above the annular locking member for engaging a top end of the annular locking member.
The first and second predetermined angles may be approximately equal such that the upper sub may be rotated relative to the lower sub into a parallel position wherein the primary longitudinal axes of the respective upper and lower subs are substantially parallel.